How to make a VI wait to execute until another one finishes

Hi all,
I have been reading the labview help for the sync functions, but I am still confused about how to perform this simple task. I have a labview program that connects to a DSP via serial (RS232). I use VISA Read and VISA Write to read to and write from the device. My goal is to first write, wait until writing is finished, then wait for, say, 100 ms (so that it is ensured that all the data has been sent correctly), and then perform the read operation.
At the moment I have VISA Write connected to VISA Read via the error out-to-error in wire. However, I am not sure that they perform one after the other correctly, so I would like to implement a more robust synchronisation.
Thank you very much in advance
Solved!
Go to Solution.

There is also another issue with the synchronous mode on VISA calls. As far as LabVIEW is concerned it is done once the data has been handed to the OS or lower level drivers. For instance, if you use the synchronous call for a VISA write on a TCP connection it will virtually always return immediately even though a trace (using something like Wireshark) clearly shows the data being delaying, buffered and sent out well after the call to the write complete. Given this is NI's position on how this call should work I imagine you could run into the same thing with other interfaces. Their position is that once they have handed the data to the lower level for delivery the call is complete, regardless of whether the data transfer actually was completed.
Even so, if you know what the data you expect back looks like you can simply use the read timeout to effectively give you the delay. Putting arbitrary delays in such as the wait 100 ms may work now but not work in the future. You are far better off to use your actual data streams to control your synchronization. This is especially true in a command/response type of protocol.
Mark Yedinak
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Wreck of the Edmund Fitzgerald - Gordon Lightfoot

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